Method of surfacing metal objects



Patented June 10, 1952 2,600,358 METHOD or SURFAOING METAL onmo'rs John W. Bolton, Hamilton, and Sylvester A. Weigand, Cincinnati, assignors to The Lunkenheimer Company, Cincinnati, Ohio, a corporation of Ohio No Drawing. Application March 15, 194A),

' Serial No. 81,634

12 Claims.

1 This invention relates to a method for improving the surface quality of castings and articles made of bronze or related metal alloys. One of the. principal obj ectives'of the invention has been to produce durable finishes upon the surfaces of such metals in order that the appearance thereof will not only identify them as to their distinctive color, but will also be durably attractive in appearance and in surface feel or quality. It has also been a primary objective of the invention to provide a technique by which such results may be attained as an incident to the removal of sand or dirt which is adherent to castings of such metals as a result of the founding thereof.

In many modern foundry operations it is conventional at the present time to utilize grit blast ing for the purpose of removing scale and oxide films and for the purpose of abrading molding or core sand from the work piece, which normally clings to it following a shake-out operation. In a typical procedure of this type, a stream of grit is projected upon the work piece, at high velocity, and the particles of grit, by impact, remove dirt and scale so as to leave the surface in a clean and bright condition. The grit in common use 'for this purpose is finely divided particles of sand,

steel, or iron, such particles being propelled at high velocity either by a stream of air or steam or water, or by projection from the periphery of a rapidly rotating impeller wheel.

When a casting made of bronze is exposed to this treatment and the adherent sand and scale have been removed, the casting presents a clean, relatively smooth, dull mat, surface which is attractive in appearance. However, this surface, during consequent machining operations is soon blemished; because of its tooth or surface roughness, particles of dirt or dust or grease cling to it tenaciously and workmen, handling the piece with dirty hands, leave smudges which are not removed conveniently even by detergent washing which is commonplace today. The mat finish also soon becomes blemished through the adherence of airborne dust to the surface while the part is in process of manufacture or in storage.

The net result of this surface quality is that the same casting or work piece which originally had a clean, uniform and attractive appearance. looks dirty and smudged in its finished form, or in the final product of which it constitutes a part. Such defects are of no consequence when the work piece is subsequently painted. However, in many products, the display of the native color of the metal is desired, as in valves, plumbing fixtures, hardware parts and the like, since the 7 having service value.

purchaser himself identifies the metal as one In recognition of this problem, the present invention is directed to a procedure by which a metal object made of bronze or similar non-ferrous metal, may be provided with an identifying surface appearance which is characteristically grit blasted, but which is durable or permanent and which does not change or become irreparably smudged or dirty during machining operations, or during storage to which the object subsequently is exposed.

Beside sand and steel grit or shot, various other abradant particles have been proposed for use in typical shot blasting operations. .Proceeding upon an assumption that some abradent less harsh than steel or sand might produce a surface of desired quality upon a casting made of bronze, we endeavored to utilize various nonferrous metals such as copper and nickel, as well as brass alloys, but the results were found to be unsatisfactory. Copper shot projected on a casting made of brass or bronze cleans the surface effectively but leaves a reddish, dark deposit which though uniform in color is much less attractive even than the smudged appearance of a bright mat surface as produced by blasting with a conventional grit. The same results were found to be produced through use of the conventional brass alloys. It is believed that such metals, being relatively soft, abrade themselves upon the surface of the work piece to leave exceedingly fine or thin deposits which display a reddish dark to almost black color, just as very finely divided copper in bulk is blackish in appearance. On the other hand, alloyshigh in nickel content, light to whitish in color, which are expensive to begin with, are so frangible that the loss of such shot in a typical abrading operation is prohibitively highand they fail to providethe result desired.

This invention is based upon the concept, determination and discovery that a durably attractive surface finish may be imparted to the bronze casting by subjecting it to a grit blasting operation in which the particles of abradant consist essentially of copper, but contain color controlling elements of which zinc and silicon are representative. Paradoxically, although copper in itself leaves a red undesirable deposit on a non-ferrous metal surface when used as ashot blast medium, shot or grit produced from an alloy consisting predominantly of copper, but containing small percentages of silicon and zinc produces surface finishes which match the color of the pa tive metal as cast or as machined. Such surfaces are characterized by an overall smoothness to the feel; hence they lack the dirt collecting qualities of a mat finish as produced by ferrous grit or sand. In general, such surfaces, though they visibly may appear to have been peened through impact of the particles of alloy abradant, are relatively slick and smooth and shed the dirt or dust which may be rubbed upon them in the production handling thereof, or the dust which may accumulate upon them during storage of the treated pieces in the bins or on the shelves of warehouses.

The evidence which is available at present points to the fact that shot or particles of copper, zinc and silicon alloy projected on the surface of a brass or bronze work piece or casting leave a film or thin skin-like deposit, the particles themselves being worn away to that extent. However, this deposit instead of being of a red or dark color which is characteristic of the copper metal of the alloy is of color matching that of bronze and conforms, therefore, to the color of the casting upon which it appears. The mat finish of a typically abraded article which has been exposed to ferrous grit or sand is exceedingly susceptible to oxidation or to chemical reaction; in contrast the smooth deposition upon the surface of a casting produced by the present technique resists color deterioration after prolonged exposure, or treatment with the alkalies and detergents commonly used in washing apparatus.

Castings made of casting alloy ASTM B61 (also known as Navy M, or steam or valve bronze) finds wide usage in valve parts, fittings and other articles and may be considered to be typical of metals adapted to be treated by the process of this invention, although other alloys, such as ASTM B62, respond favorably in so far as duplication of their color in the film deposit is concerned. The process, of course, can be applied to brasses or other metals but there is usually no advantage in doing so in view of the higher cost of the abradants of this invention over common sand or steel grit. Strangely enough, the use of B61 or B62 alloys themselves as abradants in the blasting of castings made of these same metals produces a coloration which is distinctly different from the color of these alloys in their cast form or on their machine surfaces, which illustrates the peculiar behavior that is provided by the nature of the composition of the abradant alloy.

Shot or abradant particles which have been found to be particularly useful to produce the results just described may consist of an alloy substantially as follows:

Example Per cent Silicon 3.5 Zinc 14.0 Copper 82.5

Alloys manufactured with the disclosure of Ray and Gould U. S. Patent No. 1,933,390 of October 31, 1933, are generally satisfactory, although for present purposes, the proportions of silicon and zinc are not precisely critical and satisfactory results may be obtained when zinc is within the range of approximately 5 to and silicon is Within the range of approximately 2 to 6%, the balance being copper. Small amounts of tin, lead, aluminum, manganese or iron, not exceeding about 2%, may be present in the abradant alloys; in fact, the incorporation of aluminum to the extent of 0.60% is particularly advantageous in the treatment of ASTM bronzes B61 and B62.

The particles of abradant, for best results in the treatment of the common run of castings, may be spherical or spheroidal in shape, and within the range of about 20 to A. F. A. sieve mesh. Larger pellets produce the desired effects of cleaning and coloration, but the peening effect is somewhat heavier or deeper, and this may be undesirable in the treatment of articles of relatively small size. For larger classes of castings, or for any purpose when a greater peened appearance is desired, larger pellets offer an advantage. When the particles are reduced in size to about 70 A. F. A. sieve mesh, they are slower in cleaning action, based upon an equivalent initial velocity, and when the particles are reduced to about 100 A. F. A. sieve mesh, they are so small that they tend to be dissipated or lost from the machine as dust. Of course, they are also slow in cleaning action because of the high ratio of surface area to mass.

The usual hardness range of castings consisting of ASTM B61 and B62 alloys is to 65 Brinell hardness number. Studies of effects of the hardness of the abradant alloy used to clean such castings indicate that satisfactory results are obtained when the abradant alloy has a hardness of approximately to Brinell hardness number. Where delicate lettering must be preserved in. the finished casting to be blasted, the abradant particles advantageously may be of 50 to 75 Brinell hardness number, although, in such event, there is a little loss in cleaning time. The hardness of a copper-silicon-zinc alloy abradant is adjusted easily by variation of silicon content.

Density of copper-silicon-zinc pellets of the type disclosed may be approximately 8.47 although this figure may vary; this is approximately the same density as that of a similar copper-silicon-zinc alloy when it is in the sand cast form.

In place of particles of spherical shape, excellent results may also be obtained by the use of particles in irregular or fragment form; thus, sieved chips produced by turning, boring, or by other comminution have been used with very satisfactory results.

The practice of the present invention is particularly advantageous in the surface treatment of castings made of bronze or other alloys which are to be surface finished in whole or part by turning, boring, drilling or similar machining operations. When steel or sand is used as an abradant, some particles thereof almost always are impacted into the surface of the work piece and, these being very hard, cause pronounced dulling of the cutting tools which come into contact with them. The tools, therefore, soon fail to cut efiiciently even though the native metal of the castings upon which they work is soft and freely machinable. In comparison, the treatment of castings by the method of the present invention causes the removal of adherent sand, but the abradant particles leave no hard deposits on their own. Thus, it has been our experience, as determined by a number of production operations. that tool life is increased as much as 10 to 25% or more over the life of tools used in the machining of similar castings treated by conventional abradants.

The invention is particularly useful when utilized upon dirty castings as they come from the foundry, since a durably attractive finish having a color matching the native color of the metal is produced as an incident to the removal of the clinging sand and scale. In this respect, the most satisfactory results we have obtained in the ifatmenbr 01 i e variety o o ct o' iin bodies and component parts of bronze valves, comprises an initial alloy abrad-ing treatment for removal of the major portion of the dirt, followed by grinding, snagging or chipping operations in which fins and major surface imperfections are removed. Next, a second abrading operation is employed with the alloy particles, in which the balance of the dirt is removed and a uniform surface treatment of pleasing appearance is applied to the whole surface of the Work piece, including the bright areas resulting from previous grinding or chipping operations.

'Ifhe' loss, through breakdown, deterioration and escape of particles of the-abradant alloys of copper, zinc and silicon which we have disclosed, sufficiently low to compare favorably with that of ferrous shot or fragments, despite the relatively higher cost of the non-ferrous alloy. Some dust and particles too fine to operate effectively may be collected through the apparatus which is provided in modern abrading machines, and this off-material may readily be sold as scrap, or may be reworked into pellets as disclosed in a copending patent application, filed by one of us, Sylvester A. Weigand, on August 2, 1949, U. S. patent application Serial No. 108,207,- entitled Method and Apparatus for Forming Pellets.

However, the use of the abradant particles of this invention is not confined to impeller type machines.

Surface finishes of the quality described may be obtained by a projection of the particles through a velocity air stream or by steam or liquid blast. Thus, the .term blasting or abrading, as used throughout this specification and in the claims, is intended to embrace the projection of the alloy particles or shot at high speed against the surfaces which are to be cleaned or treated, whether these surfaces contain adherent sand or dirt, or whether they are merely being treated to improve the appearance thereof.

Having described our invention, we claim:

1. A method of imparting to the surface of an object made of bronze alloy, a durable, attractive finish having a color substantially matching the color of the native bronze metal, which method comprises; subjecting the surface of such object to a velocity stream of abradant particles consisting essentially of an alloy of copper, silicon, and zinc, in which abradant alloy the copper constitutes the predominant component and the silicon and zinc are sufficient in amount to impart to the minute deposits thereof which are left upon the surface of the object by their abrasion a color substantially like that of the native bronze metal of the object.

2. The method of removing adherent sand and scale from a bronze casting and simultaneously imparting a durable surface finish thereon which is of the appearance of the metal of the casting, said method comprising; exposing the surface of the said casting to the impingement of particles of an alloy consisting essentially of copper, but containing smaller proportions of zinc and silicon, the said particles being directed at the said casting at such a velocity that they abrade themselves upon the surface of the casting and leave a deposit of bronze color thereon in so doing.

3. In the art of grit blasting objects in the form of bronze alloy castings, that improvement which consists in directing particles of an alloy of copper, zinc and silicon, in which the zinc the alloy and the silicon comprises approximately 2 to 6% by weight, the balance being-substantially all copper, at high velocity, upon the surface of such a casting, whereby the particles, by their own abrasion attendingimpact' with the surface of the casting, leave an adherent deposit thereon which is of characteristic bronze color.

4. In the manufacture of articles: from cuprous bronze-like castings, the method of producing a durable, attractive finish upon the surfaces of said castings of color matching that of the. native metal of the castings, which method comprises; subjectingsaid castings to surface abrasion by directing upon surfaces thereof. a high velocity stream containing particles of an. alloy comprising, by weight, about ;82'. 5% of copper, about 14.0% of zinc, and about 3.5% Of silicon.

5. A methodof imparting to the surface of an object made of a cuprous alloy having substantially the color of ASTM. B61 alloy, a durable attractive finish which is substantially of matching color, said method comprising; subjecting the said object to a velocity stream of spheroid particles of metal consisting essentially .ofan alloy of copper, silicon and zinc in which alloy the copper constitutes the predominant. component, while the silicon and zinc are sufiicient in amount to impart a bronze color cast to the minute deposits thereof which are left upon the surface of the article by their abrasion.

6. A method of imparting a durable,-attractive finish upon the surface of a non-ferrous, cuprous alloy, which method comprises; subjecting the surface of such metal to a velocity stream of irregularly shaped fragment particles of metal consisting essentialy of an alloy of copper, silicon and zinc, in which alloy the copper constitutes the predominant component and the silicon and zinc are sufiicient in amount to impart a brass-like cast to the minute deposits thereof which are left upon the surface of the article by their abrasion.

7. A method of imparting to the surface of an object made of bronze alloy a durable surface finish having a color substantially matching the color of the native metal of the object, which method comprises; subjecting the surface of the object to a velocity stream of abradant particles ranging in size from about 20 to 50 A. F. A. sieve mesh, the said particles consisting essentially of particles of an alloy of copper, silicon and zinc in which copper constitutes the predominant component, while the silicon and zinc are sufiicient in amount to impart to minute film-like deposits of alloy which are left upon the surface of the object by their abrasion, a color substantially like that of'th e native metal of the object.

8. A method of imparting to the surface of an article made of bronze alloy a durable surface finish having a color substantially matching the color of the native metal of the object, said method comprising; subjecting the surface of such object to a velocity stream of abradant particles consisting essentially of an alloy of copper, silicon and zinc having a Brinell hardness number of approximately 50 to in which alloy the copper constitutes the predominant component and the silicon and zinc are sufficient in amount to impart to minute deposits of the alloy which are left upon the surface of the object by abrasion of the particles, a color substantially like that of the native metal of the object.

9. A method of imparting to the surface of an object made of a cuprous alloy which displays substantially the color of AS'I'M B61 alloy a durable attractive finish which is substantially of matching color, said method comprising; subjecting the surface of the object to a velocity stream of particles of metal having a Brinell hardness number of 50 to 100 the said particles consisting essentially of an alloy of copper, silicon and zinc in which the copper constitutes the predominant component while the silicon and -zinc are sufficient in amount to impart a bronze color to minute deposits thereof which are left upon the surface of the object by abrasion of said particles.

10. A method of imparting to the surface of an object made of a cuprous alloy which displays substantially the color of ASTM B61 alloy a durable attractive finish which is substantially of matching color, said method comprising; subjecting the surface of the object to a velocity stream of particles of metal having a Brinell hardness number of 75 to 100, the said particles consisting essentially of an alloy of copper, silicon and zinc in which the copper constitues the predominant component while the silicon and zinc are sufficient in amount to impart a bronze color to minute deposits thereof which are left upon the surface of the object by abrasion of said particles.

11. A method of imparting to the surface of an object made of a cuprous alloy which displays substantially the color of ASTM B61 alloy a durable attractive finish which is substantially of matching color, said method comprising; subjecting the surface of the object to a velocity stream of particles of metal having a Brinell hardness number of 50 to 100, the said particles consisting essentially of an alloy of copper, silicon and zinc in which the copper constitutes the predominant component while the silicon and zinc are sufiicient in amount to impart a bronze color to minute deposits thereof which are left upon the surface of the object by abrasion of said particles, the said particles being within the range of approximately 20 to 50 A. F. A. sieve mesh.

12. In the art of grit blasting objects which are in the form of cuprous alloy castings, the improvement which consisting in directing particles of an alloy comprising approximately 5 to 20% by weight of zinc, 2 to 6% by weight of silicon, approximately 0.6% by weight of aluminum, the balance being substantially all copper, at high velocity, upon the surface of such a casting, whereby the particles, by their own abrasion attending impact with the surface of the casting leave an inherent deposit thereon which is of characteristic bronze color.

JOHN W. BOLTON. SYLVESTER A. WEIGAND.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,933,390 Ray Oct. 31, 1933 2,269,219 Miller Jan. 6, 1942 

1. A METHOD OF IMPARTING TO THE SURFACE OF AN OBJECT MADE TO BRONZE ALLOY, A DURABLE, ATTRACTIVE FINISH HAVING A COLOR SUBSTANTIALLY MATCHING THE COLOR OF THE NATIVE BRONZE METAL, WHICH METHOD COMPRISES; SUBJECTING THE SURFACE OF SUCH OBJECT TO A VELOCITY STREAM OF ABRADANT PARTICLES CONSISTING ESSENTIALLY OF AN ALLOY OF COPPER, SILICON, AND ZINC, IN WHICH ABRADANT ALLOY THE COPPERCONSTITUTES THE PREDOMINANT COMPONENT AND THE SILICON AND ZINC ARE SUFFICIENT IN AMOUNT TO IMPART TO THE MINUTE DEPOSITS THEREOF WHICH ARE LEFT UPON THE SURFACE OF THE OBJECT BY THEIR ABRASION A COLOR SUBSTANTIALLY LIKE THAT OF THE NATIVE BRONZE METAL OF THE OBJECT. 